التفاصيل البيبلوغرافية
| العنوان: |
Perspective on Kramers symmetry breaking and restoration in relativistic electronic structure methods for open-shell systems. |
| المؤلفون: |
Kasper, Joseph M., Jenkins, Andrew J., Sun, Shichao, Li, Xiaosong |
| المصدر: |
Journal of Chemical Physics; 9/7/2020, Vol. 153 Issue 9, p1-11, 11p |
| مصطلحات موضوعية: |
SYMMETRY breaking, ELECTRONIC structure, EXCITED states, MAGNETIC fields, SYMMETRY |
| مستخلص: |
Without rigorous symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of the relativistic electronic structure, if time-reversal symmetry is not enforced in calculations of molecules not subject to a magnetic field, it is possible to artificially break Kramers degeneracy in open shell systems. This leads to a description of excited states that may be qualitatively incorrect. Despite this, different electronic structure methods to incorporate correlation and excited states can partially restore Kramers degeneracy from a broken symmetry solution. For single-reference techniques, the inclusion of double and possibly triple excitations in the ground state provides much of the needed correction. Formally, however, this imbalanced treatment of the Kramers-paired spaces is a multi-reference problem, and so methods such as complete-active-space methods perform much better at recovering much of the correct symmetry by state averaging. Using multi-reference configuration interaction, any additional corrections can be obtained as the solution approaches the full configuration interaction limit. A recently proposed "Kramers contamination" value is also used to assess the magnitude of symmetry breaking. [ABSTRACT FROM AUTHOR] |
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